Process for producing organic acids

ABSTRACT

An improvement in a process for converting an unsaturated, acyclic hydrocarbon to a carboxylic acid in which the unsaturated, acyclic hydrocarbon is reacted with oxygen containing a small amount of ozone at a low temperature to obtain an intermediate product in a first stage and the intermediate product is oxidized in a second stage with molecular oxygen at a higher temperature to obtain the desired carboxylic acid, which involves employing a solvent mixture comprising a major amount of a carboxylic acid solvent having a boiling point as high or higher than the highest boiling point of a carboxylic acid formed during the reaction and a minor amount of lower carboxylic acid solvent or a lower alcohol solvent, whereby fogging during the first stage of the process is reduced.

United States Patent Ellis et al.

[ 1 Sept. 12,1972

[54] PROCESS FOR PRODUCING ORGANIC ACIDS [72] Inventors: Alan F. Ellis,Murrysville; Richard Seekircher, Cheswick, both of Pa.

[73] Assignee: Gulf Research 8: Development Com- [22] Filed: Jan. 13,1971 21 Appl, No.: 106,286

[52] US. Cl. ..260/533 R, 260/413 [51] Int. Cl. ..C07c 51/00, C070 51/32[58] Field of Search ..260l533 R, 413

[56] References Cited FOREIGN PATENTS OR APPLICATIONS 66l,797 3/1963Canada ..260/533 R Primary Examiner-Lorraine A. Weinberger AssistantExaminer-Richard D. Kelly Attorney-Meyer l-leishloss, Deane E. Keith andJoseph J. Carducci [5 7] ABSTRACT An improvement in a process forconverting an unsaturated, acyclic hydrocarbon to a carboxylic acid inwhich the unsaturated, acyclic hydrocarbon is reacted with oxygencontaining a small amount of ozone at a low temperature to obtain anintermediate product in a first stage and the intermediate product isoxidized in a second stage with molecular oxygen at a higher temperatureto obtain the desired carboxylic acid,

14 Claims, No Drawings PROCESS FOR PRODUCING ORGANIC ACIDS Thisinvention relates to a process for converting an unsaturated, acyclichydrocarbon to an organic carboxylic acid by using ozone an oxygen. Morespecifically, this invention relates to an improvement in the processwherein an unsaturated, acyclic hydrocarbon is subjected to ozonolysisin a first stage while the same is dissolved in a solvent mixturecontaining a minor amount of a lower organic carboxylic acid solvent ora lower alcohol solvent.

Unsaturated, acyclic hydrocarbons that can be used herein as charge caninclude straight or branched chain olefins, terminal as well asinternal, having from five to 12 carbon atoms, preferably from six to 10carbon atoms. Specific examples of olefins that can be used arepentene-l, octene-l, octene-l,2, dodecene-3, decene- 5,3-methylpentene-l 3-ethyldecene-3, etc.

The ozonolysis procedure used in the first step follows the conventionaloutline. Thus, for example, a stream of gas containing molecular oxygen,such as oxygen itself and from about 0.5 to about 6, or even higher, butpreferably about 2 to about 3 per cent, by weight of ozone relative tooxygen is passed continuously through the olefin charge dissolved in aunique solvent mixture, to be defined hereinafter, at such a rate sothat the exit stream will be substantially free of ozone, continuinguntil some ozone is found in the exit gas, at which time the ozonolysisreaction will have terminated. Since ozonolysis is substantiallyinstantaneous, the time of contact depends upon obtaining suitablecontact between ozone and unreacted olefin. The temperature can be fromabout -20 C. to about 35 C., preferably about 10 C. to about 20 C., andwhile pressure as high as about 50 pounds per square inch gauge can beemployed, atmospheric pressure is preferred. As a result of ozonolysis,cleavage of the olefinic double bond occurs to form aldehydes andhydroperoxides. Thus, the olefin for example, R and R" being alkylsubstituents, is believed to be converted to 1* RC=O and R(lJ-OH whereinR represents an alkyl group in the case of an alcohol solvent and anacyl group in the case of an acid solvent. The hydroperoxide is believedto result from the addition reaction of the intermediate Zwitterion witha component of the solvent mixture used herein.

The aldehydes and hydroperoxides so produced are then subjected tooxidation in a second stage with a gas containing molecular oxygen,preferably air. Any effective method which insures contact between thealdehyde and the hydroperoxide and oxygen can be used. In a preferredembodiment air is continuously passed through the ozonolysis product andthis is preferably continued until there is no noticeable reduction inoxygen content of the exit stream. The amount of oxygenstoichiometrically needed, relative to the ozonolysis product, definedas consisting essentially of aldehydes and hydroperoxides, on a molarbasis must be at least about 0.5:1, but in general from about 5:1 toabout 100:1, is used. Temperatures of about C. to about 150 C.,preferably about C. to about 110 C., can be used. Pressures as high asabout pounds per square inch gauge can be employed, but in generalatmospheric pressure is preferred. A reaction time of about 0.5 to abouttwo hours will generally suffice. As a result of the oxidation step itis believed the aldehydes are oxidized and the hydroperoxides arerearranged to the corresponding organic carboxylic acids. Recovery ofthe organic carboxylic acids from the reaction mixture can be effectedin any desired manner, but in general fractional distillation ispreferred.

In order to assist in the recovery, by distillation, of the productcarboxylic acids from the reaction product at the end of the secondstage, we intend to use a solvent mixture containing a major amount ofan organic carboxylic acid solvent having a boiling point as high, orhigher, than the highest boiling point of the organic carboxylic acidsproduced herein. This is so because the organic carboxylic acidsproduced can then be distilled from the reaction mixture, leaving behindthe high-boiling organic carboxylic acid solvent which can then berecycled for reuse in a subsequent oxidation process. If an organiccarboxylic acid, such as acetic acid, having a boiling point lower thanthe organic carboxylic acids produced were used, recovery of the productorganic carboxylic acids could not begin until all said lower-boilingcarboxylic acid is first distilled therefrom. Moreover, near the end ofthe distillation period, recovery of the last of the desired organiccarboxylic acid product from any small amount of heavier by-productsthat might be present-would be difficult without the addition of achaser thereto.

Unfortunately, we have found that the use of the defined high-boilingorganic acid solvent in the ozonolysis procedure employed in the firststep results in a potentially hazardous fog. These conditions could giverise to explosive mixtures. We have found that such fogs can besubstantially reduced by adding a minor amount of a lower organiccarboxylic acid solvent or a lower alcohol solvent to the definedhigh-boiling carboxylic acid solvent. Of course, during the distillationrecovery period such added organic carboxylic acid or lower alcoholcould come off prior to the desired organic carboxylic acid product andreused, but since the amounts used are small no significant increase inoperating expense would be entailed thereby.

The organic carboxylic acid solvent having a boiling point as high, orhigher, than the organic carboxylic acids produced herein, can bedefined as having from five to 10 carbon atoms, preferably from six tonine carbon atoms. Specific examples of such organic carboxylic acidsare alkanoic acids such as hexanoic acid, heptanoic acid, octanoic acid,nonanoic acid, decanoic acid, 2-methylhexanoic acid, S-methyloctanoicacid,

etc. The lower organic carboxylic acid solvents that are added to theorganic carboxylic acid solvent are the alkanoic acids formic acid,acetic acid and propionic acid, while the alcohols are the alkanols,methanol, ethanol, normal propanol and isopropanol. The amount of higherboiling carboxylic acid solvent used, based on the total reactionmixture, can be from about 50 to about 95 per cent by weight, preferablyfrom about 65 to about 85 per cent by weight. The amount of lowercarboxylic acid solvent added to the higher boiling point carboxylicacid solvent, based on the total reaction mixture, can be from about 1to about per cent by weight, preferably from about 2 to about 5 per centby weight, while the amount of lower alcohol solvent can be from about 5to per cent by weight, preferably from about 7 to 10 per cent by weight.

The process defined herein can further be illustrated by the following.

EXAMPLE I Thirty grams of an internal olefin mixture containing 91 percent by weight of decene-S was dissolved in 70 grams of pelargonic acidand oxidized at to C. and atmospheric pressure by passing oxygencontaining from 2 to 3 per cent by weight of ozone through the mixtureat the rate of 1 liter per minute over a period of about 2 hours. Duringthe ozonization a heavy fog was observed in the vapor phase. After theozone take-up was completed the mixture was heated to 120 while oxygenwas passed therethrough at the rate of 1 liter per minute over a periodof 2 hours. During the heat-up period the temperature increased to about170 C. for a short time in a violent reaction. The temperaturesubsequently returned to 120 C. The product obtained was found tocontain mainly pentanoic acids.

EXAMPLE II The experiment of EXAMPLE I was repeated, except that 5 gramsof propionic acid was added to the reaction mixture prior toozonization. Only a slight amount of fog was noted, and the temperatureduring oxidation rose to only 150 C.

EXAMPLE III The experiment of EXAMPLE I was again repeated, except thatfour grams of acetic acid was added to the reaction mixture prior toozonization. Only a slight amount of fog was noted, and the temperatureduring the subsequent oxidation step rose to only 140 C.

EXAMPLE IV When the experiment of EXAMPLE I was repeated, but with 4grams of formic acid also present initially, only traces of fog werenoted and the temperature during oxidation rose to only 140 C.

EXAMPLE V Repeating the experiment of EXAMPLE I, but with 5 grams ofmethanol also present, fog was reduced slightly. When 10 grams ofmethanol was used only traces of fog was noted. In each case thetemperature during oxidation rose to 130 C.

EXAMPLE VI The experiment of EXAMPLE I was repeated, except that tengrams of normal propanol was also present in the initial reactionmixture. There was noted a slight decrease in fog, and the temperatureduring the oxidation was reduced to 120 C.

EXAMPLE VII Thirty grams of a blend of internal olefins of a carbonrange of C to C was dissolved in grams of pelargonic acid. Theozonization and oxidation were performed in the same manner as inEXAMPLE I. A heavy fog was observed and the temperature during theoxidation rose to 155 C.

EXAMPLE VIII When the experiment of EXAMPLE VII was ,repeated, but withten grams of formic acid also present initially, only a slight amount offog was noted and the temperature during the oxidation step rose to nohigher than 135 C.

EXAMPLE IX Repeating the experiment of EXAMPLE VII, but with 10 grams ofmethanol present initially, only a slight amount of fog was noted, andthetemperature rose to 120 C.

Obviously, many modifications and variations of the invention, ashereinabove set forth, can be made without departing from the spirit andscope thereof, and therefore only such limitations should be imposed asare indicated in the appended claims.

We claim:

1. In a process for converting an unsaturated, acyclic hydrocarbonhaving from five to 12 carbon atoms to a carboxylic acid wherein theunsaturated, acyclic hydrocarbon in reacted with ozone at a lowtemperature of about 20 C. to about 35 C. to obtain an intermediateproduct in a first stage and the intermediate product is oxidized in asecond stage with molecular oxygen at a higher temperature of about 70C. to about 150 C. to obtain the desired carboxylic acid, theimprovement which comprises carrying out the process in a solventmixture comprising a major amount of an alkanoic acid solvent havingfrom five to 10 carbon atoms and a boiling point as high or higher thanthe highest boiling point of a carboxylic acid formed during thereaction and a minor amount of a lower alkanoic acid solvent having fromone to three carbon atoms or a lower alkanol solvent having from one tothree carbon atoms.

2. The process of claim 1 wherein the hydrocarbon charge has from six to10 carbon atoms, the reaction with ozone in the first stage is carriedout at a temperature of about 10 C. to about 20 C., the oxidation in thesecond stage is carried out at a temperature of about C. to about C. andsaid higher boiling carboxylic acid solvent has from six to nine carbonatoms.

3. The process of claim 1 in which said higher boiling carboxylic acidsolvent has from six to nine carbon atoms.

4. The process of claim 1 in which said higher boiling carboxylic acidsolvent is pelargonic acid.

5. The process of claim 1 in which said lower carboxylic acid solvent isformic acid.

6. The process of claim 1 in which said lower carboxylic acid solvent isacetic acid.

7. The process of claim 1 in which said lower carboxylic acid solvent ispropionic acid.

8. The process of claim 1 in which the lower alcohol solvent is ethanolor isopropanol.

9. The process of claim 1 in which the lower alcohol solvent ismethanol.

10. The process of claim 1 in which the lower alcohol solvent is normalpropanol.

11. The process of claim 1 in which the amount of said higher boilingcarboxylic acid solvent is from about 50 to about 95 per cent by weight,based on the total reaction mixture, and the amount of said lowercarboxylic acid solvent is from about 1 to about per cent by weightbased on the total reaction mixture.

12. The process of claim 1 in which the amount of cohol solvent is fromabout 5 to about 15 per cent by weight based on the total reactionmixture.

14. The process of claim 1 in which the amount of said higher boilingcarboxylic acid solvent is from about 65 to about per cent by weight,based on the total reaction mixture, and the amount of said loweralcohol solvent is from about 7 to about 10 per cent by weight based onthe total reaction mixture.

2. The process of claim 1 wherein the hydrocarbon charge has from six to10 carbon atoms, the reaction with ozone in the first stage is carriedout at a temperature of about 10* C. to about 20* C., the oxidation inthe second stage is carried out at a temperature of about 80* C. toabout 110* C. and said higher boiling carboxylic acid solvent has fromsix to nine carbon atoms.
 3. The process of claim 1 in which said higherboiling carboxylic acid solvent has from six to nine carbon atoms. 4.The process of claim 1 in which said higher boiling carboxylic acidsolvent is pelargonic acid.
 5. The process of claim 1 in which saidlower carboxylic acid solvent is formic acid.
 6. The process of claim 1in which said lower carboxylic acid solvent is acetic acid.
 7. Theprocess of claim 1 in which said lower carboxylic acid solvent ispropionic acid.
 8. The process of claim 1 in which the lower alcoholsolvent is ethanol or isopropanol.
 9. The process of claim 1 in whichthe lower alcohol solvent is methanol.
 10. The process of claim 1 inwhich the lower alcohol solvent is normal propanol.
 11. The process ofclaim 1 in which the amount of said higher boiling carboxylic acidsolvent is from about 50 to about 95 per cent by weight, based on thetotal reaction mixture, and the amount of said lower carboxylic acidsolvent is from about 1 to about 10 per cent by weight based on thetotal reaction mixture.
 12. The process of claim 1 in which the amountof said higher boiling carboxylic acid solvent is from about 65 to about85 per cent by weight, based on the total reaction mixture, and theamount of said lower carboxylic acid solvent is from about 2 to about 5per cent by weight based on the total reaction mixture.
 13. The processof claim 1 in which the amount of said higher boiling carboxylic acidsolvent is from about 50 to about 95 per cent by weight, based on thetotal reaction mixture, and the amount of said lower alcohol solvent isfrom about 5 to about 15 per cent by weight based on the total reactionmixture.
 14. The process of claim 1 in which the amount of said higherboiling carboxylic acid solvent is from about 65 to about 85 per cent byweight, based on the total reaction mixture, and the amount of saidlower alcohol solvent is from about 7 to about 10 per cent by weightbased on the total reaction mixture.